The local aboriginal peoples call the island Boambilly, or perhaps Bo-a-millie. The name Shark Island is from its shape, which is claimed to resemble a shark.

The island measures some 250 metres by 100 metres. Parts were set aside as a recreation reserve as early as 1879 and it was also used as an animal quarantine station and naval depot up until 1975. At that time it became exclusively a recreation reserve and part of the Sydney Harbour National Park. Approved operators and a scheduled ferry service take people to the island.

Just north of the northern tip of the island is Shark Island Light, an active pile lighthouse which was built in 1913. The lighthouse is painted white. It is very close to the island, about fifteen to twenty metres away.